\begin{tikzpicture}[>=Stealth]
    \coordinate [label=180:$A$] (A) at (0, 0);
    \coordinate [label=0:$B$] (B) at (5, 0);
    \coordinate [label=90:$C$] (C) at (9/5, 12/5);
    \draw [name path=ab] (A) -- (B);
    \draw [name path=ac] (A) -- (C);
    \draw [name path=bc] (B) -- (C);

    % 求角A的角平分线
    \coordinate (ma) at (2, 0);
    \path [name path=arcA] (ma) arc (0:90:2);
    \path [name intersections={of=arcA and ac, by={na}}];
    \path [name path=arcMA] (ma)+(2,0) arc (0:90:2);
    \path [name path=arcNA] (na)+(30:2) arc (30:-60:2);;
    \path [name intersections={of=arcMA and arcNA, by={pa}}];
    \path [name path=splitA] (A) -- (pa);

    % 求角B的角平分线
    \coordinate (mb) at (3, 0);
    \path [name path=arcB] (mb) arc(180:90:2);
    \path [name intersections={of=arcB and bc, by={nb}}];
    \path [name path=arcMB] (mb)+(-2,0) arc(180:90:2);
    \path [name path=arcNB] (nb)+(120:2) arc (120:220:2);
    \path [name intersections={of=arcMB and arcNB, by={pb}}];
    \path [name path=splitB] (B) -- (pb);

    % 根据两角的平分线，确定内切圆的圆心
    \path [name intersections={of=splitA and splitB, by={O}}];
    \node [anchor=south] at (O) {$O$};

    % 绘制内切圆
    \coordinate [label=270:$D$] (D) at (A -| O);
    \draw (O) let
                \p1 = ($ (O) - (D) $)
              in
                circle ({veclen(\x1,\y1)});

    % 其它
    \draw [dashed] (A) -- (O) -- (B) (O) -- (D);
    \node at (2.2, 0.4) {$r$};
    \node at (3.2, -0.2) {$c$};
\end{tikzpicture}